This invention relates to solar control glazing, particularly, but not exclusively, for architectural applications.
Solar control glazing may be used to control one or more of the following properties of a glazing panel:                a) direct energy transmittance (DET) i.e. the proportion of the solar energy transmitted directly through a substrate as a percentage of the incident solar energy;        b) solar factor (SF) i.e. the solar energy that is transmitted through a substrate (including the energy absorbed by the substrate and emitted by the substrate towards the interior) as a percentage of the incident solar energy;        c) luminous transmittance (LT) i.e. the luminous flux transmitted through a substrate as a percentage of the incident luminous flux;        d) luminous reflectance (RL) i.e. the luminous flux reflected from a substrate as a percentage of the incident luminous flux;        e) selectivity i.e. the ratio of the luminous transmittance to the solar factor (LT/SF).        f) purity (p) of the colour i.e. the excitation purity specified according to a linear scale on which a defined white light source has a purity of zero and the pure colour has a purity of 100%. The purity of the coated substrate is measured from the side opposite the coated side.        g) dominant wavelength (λD) i.e. the peak wavelength in the range transmitted or reflected by the substrate.        
These and other properties of glazing panels as referred to herein are based on the standard definitions of the International Commission on Illumination—Commission Internationale de l'Eclairage (“CIE”). Unless otherwise stated, values herein are given with respect to standard CIE illuminant C (which represents average daylight having a colour temperature of 6700°K) for a clear, approximately 6 mm thick glass substrate arranged as a single glazing sheet. The colour co-ordinates referred to herein are measured on the Hunter scale.
Solar control glazing usually consists of a glass substrate which carries a solar filter. One particular known type of solar filter consists of the following layers (in order):
1) a metal oxide layer 200 Å to 400 Å thick
2) an infra-red reflecting metal layer 50 Å to 200 Å thick
3) a barrier layer
4) a metal oxide layer 400 Å to 800 Å thick
5) an infra-red reflecting metal layer 50 Å to 200 Å thick
6) a barrier layer
7) a metal oxide layer 200 Å to 400 Å thick
The thicknesses of the various layer can be varied over a wide range and the figures given above are merely to indicate a general order of magnitude.